Question

Yeast poison themselves to death, because

• A. Above 13% of alcohol is hazardous.
• B. Above 13% of lactic acid is hazardous.
• C. Above 13% of pyruvic acid is hazardous.
• D. Low energy produced cannot support their growth.

Hint:

Yeasts die from their own alcohol production if ethanol levels exceed 13%, due to membrane and enzyme disruption.

Answer 1

The Correct Option is A

Yeasts, especially \textit{Saccharomyces cerevisiae}, perform fermentation to produce ethanol (alcohol) and carbon dioxide from sugars under anaerobic conditions. However, alcohol at high concentrations becomes toxic to yeast cells themselves. When the concentration of ethanol exceeds 13%, it disrupts the integrity of the yeast cell membrane, denatures proteins, and interferes with vital metabolic processes. This self-generated ethanol buildup effectively poisons the yeast, leading to cell death, which is why industrial ethanol production rarely goes beyond this threshold without using ethanol-tolerant strains or distillation processes.

Answer 2

Yeast poison themselves to death, because:

Yeast cells ferment sugars to produce alcohol (ethanol) and carbon dioxide. However, ethanol is toxic to yeast cells when its concentration rises beyond a certain limit.

Specifically, when the alcohol concentration in the fermentation medium exceeds about 13%, it becomes hazardous for the yeast cells. High ethanol levels disrupt the cell membrane integrity and inhibit vital cellular processes.

As a result, yeast cells start dying or become inactive because they cannot tolerate the toxic effects of accumulated alcohol.

This phenomenon limits the natural alcohol content in beverages produced by yeast fermentation.

Correct Answer: Above 13% of alcohol is hazardous.